Violet-green Swallow Tachycineta thalassina This information was scanned from The Birds of British Columbia (Campbell et al.), Volume III, pages 144-151. Volumes I, II and III of The Birds of British Columbia can be ordered electronically at: orders@ubcpress.ubc.ca from UBC Press in Vancouver, British Columbia.

 

Range Breeds from central Alaska and Yukon, southwestern Mackenzie, northern British Columbia, southwestern Alberta, and Saskatchewan south through the western United States to Baja California and southern Mexico. Winters from central coastal California to southern Mexico and northern Central America.

Status Status is complex. On the coast, common to very abundant spring migrant on southeastern Vancouver Island and the entire lower Fraser River valley in the Georgia Depression Ecoprovince. Fairly common to very common summer visitant and autumn migrant there; occasionally abundant in autumn and very rare in early winter. Uncommon to locally common migrant and summer visitant to Western Vancouver Island and the southern and northern portions of the Coast and Mountains Ecoprovince; very rare transient on the Queen Charlotte Islands. In the interior, fairly common to very common (occasionally abundant) spring migrant and summer visitant to the south-central portions of the province, including the Southern Interior and Southern Interior Mountains ecoprovinces; common to abundant (occasionally very abundant) autumn migrant; casual in winter there. Northward, throughout the rest of the province, uncommon to locally common migrant and summer visitant except in the extreme northeastern corner, where it is a casual spring transient in the Taiga Plains Ecoprovince. Breeds.

Status Change No change.

Nonbreeding The Violet-green Swallow is widely distributed across southern British Columbia except for the west coast of Vancouver Island and the central mainland coast, where it is localized and scarce in some years. It is less numerous through the Cariboo and Chilcotin areas, and its distribution is further reduced in the northern parts of the province. Unlike the Tree Swallow, the Violet-green Swallow seldom appears on the Queen Charlotte Islands or in the Taiga Plains, and then only during migration. The Violet-green Swallow occurs from near sea level to 1,400 m elevation. Migrating flocks closely follow rivers, lakes, and valley bottoms as they move northward during the spring migration before dispersing into breeding areas. Both on the coast and in the interior, it seems to favour lowland areas with open terrain and concentrations of flying insects, on which it feeds. It is usually found over freshwater habitats, including large and small lakes, rivers, marshes, bogs, wet meadows, and beaver ponds; adjacent forest is also used. This swallow forages from low over water or ground surfaces to heights of 100 m or more above a forest canopy. The Violet-green Swallow occurs less frequently along the coast except over estuaries, where it can be found in brackish meadows, mudflats, fields, and grassy beaches. Rural and urban areas are also used, particularly agricultural pastures and well-treed suburbs. In the early spring, sunny cliff faces may also provide important foraging sites. The timing of the spring migration varies widely between years. Violet-green Swallows are among the earliest returning swallows and are particularly dependent on weather conditions, which determine the timing of insect hatches. In exceptionally mild winters, the occasional bird can arrive at the south coast in early February, and in some years the first flocks arrive in late February. Normally, however, large numbers of Violet-green Swallows appear suddenly on the Fraser River delta and southeastern Vancouver Island in March, and increase through April. These are birds in passage. Their numbers decline abruptly in May and drop further in June and July. A similar trend is evident from other areas along the coast. The coastal movement peaks about 2 weeks ahead of migration through the southern interior. In southern portions of the interior, birds may arrive in late February and early March; their numbers peak in April and then decline. Spring migration through the Southern Interior and Southern Interior Mountains is smaller and less spectacular than the coastal movement. In the Cariboo and Chilcotin areas of the Central Interior, the peak movement occurs in the second and third weeks of April. Few birds move through the Sub-Boreal Interior. In the northern interior, early arrivals occur in mid to late April, becoming most numerous in early May. In spring, the Violet-green Swallow usually migrates in flocks of 20 to 200 birds, although flocks of thousands can occur. Of 86 aggregations with more than 200 birds, 84% occurred in the Georgia Depression, 2% in the Southern Interior, 13% in the Southern Interior Mountains, and 1% elsewhere. During peak spring movements, large numbers may accumulate in good foraging areas. For example, all records of more than 1,000 birds are from lakes, all in the extreme south. The 5 maximum counts (2,500 to 9,000 birds) were all recorded in April or the first week of May, at Beaver and Elk lakes, north of Victoria. The highest total count of Violet-green Swallows in the province is 11,000 birds, tallied near Victoria at Elk, Beaver, and Prospect lakes on 15 April 1970 (Tatum 1971). Southeastern Vancouver Island has the largest spring movements in the province. Post-breeding flocks congregate over larger lakes, rivers, and marshes in July and August before moving southward. During midsummer, mixed flocks of swallows, numbering hundreds of birds, are common sights over interior lakes. The autumn migration is more protracted than the spring movement and involves smaller flocks of Violet-green Swallows. Peaks vary between years, but generally their movements begin earlier than those of other swallows. Numbers recorded on the southern migration also suggest different behaviour than during the spring movement. On the coast, where there is such a dramatic northern movement in spring, swallows depart almost unnoticed in autumn, and most have left by the first week of October. In the southern portions of the interior, however, almost the reverse is true. Of 24 autumn flocks of 200 birds or more, only 12% were from the south coast while 88% were from the southern portions of the interior. In the northern and central regions, migration begins shortly after nesting ends. The highest numbers occur in July, and most birds have gone by early to mid-August. In the Okanagan, Kootenay, and Columbia valleys, the highest numbers occur in August and September, and most birds have gone by the first week of October. In the Okanagan valley, the autumn migration peaks in early September (Cannings et al. 1987). Almost all Violet-green Swallows have left the province by the end of September. The pattern of records suggests different routes for spring and autumn migration. In spring, most Violet-green Swallows move northward along the coast, taking advantage of the milder weather and available food. The small number of birds that migrate in spring up the valleys of the southern portions of the interior suggests that the nesting population in the Central Interior and beyond is derived from the large coastal concentrations that move into the interior along major west-east river valleys. Following the breeding season, coastal birds leave shortly after their young fledge and no noticeable concentrations occur. For birds in the interior, there is no advantage in returning to the coast. Swarms of late-summer chironomids and other flying insects create an abundant supply of food over lakes and ponds. Observations of large numbers indicate that the swallows leave through the Okanagan, Creston, and other southern valleys. Mountain passes and montane areas (e.g., Manning Park) may also be important autumn migration corridors, but their use has not been well documented. Although migrating swallows spend much of their time on the wing, perching and roosting sites are important habitat components. Frequently, they use snags, leafless trees or branches, and roots protruding from eroding river banks. In rural and urban areas, telephone lines, buildings, wire fences, and bridges also provide perching sites.  On the coast, the Violet-green Swallow has been reported every month of the year, although it occurs in substantial numbers only from late February to late September. In the interior, it has been reported from 19 February to 8 November.

Breeding Nests Eggs Nest Success The Violet-green Swallow breeds throughout most of its range in the province. It is scarce in the Peace Lowland and in the Northern Boreal Mountains. The northernmost breeding records are from the Tatshenshini River, Atlin, Fireside, and Sulphur Creek, along the northern boundary of the province. There is a vast area west of the Rocky Mountains and north of the latitude of Fort St. John where there have been few observers and thus few nest records. For example, although Swarth (1922) found them abundant at Telegraph Creek, there are no other nesting records in the Stikine River drainage. There are just 3 nesting records on the coast north of Vancouver Island: Owikeno Lake, Kitsumkalum Lake, and Alice Arm. The centre of breeding abundance for the Violet-green Swallow is in the Georgia Depression, Southern Interior, and Southern Interior Mountains, where it has adapted well to human-influenced habitats. Breeding has not been reported from the Queen Charlotte Islands or the Taiga Plains. This species reaches its highest numbers on southeastern Vancouver Island and in the lower Fraser River valley of the Georgia Depression. An analysis of Breeding Bird Surveys for the period 1968 through 1993 could not detect a net change in numbers on either coastal or interior routes. Both Robbins et al. (1986) for North America and Erskine et al. (1992) for southern British Columbia also note stable Violet-green Swallow populations.  On the coast, the Violet-green Swallow has been found breeding from near sea level to 390 m elevation; in the interior, it breeds from 300 to 1,400 m elevation. It seems to thrive in close association with humans (Weber 1972; Allen et al. 1977). Over 75% of 847 nests were from human-associated habitats. Most nests (62%; n = 805) were found in backyard gardens and residential buildings, roadside habitats, meadows, or shorelines (lakes, streams, marshes, seashores). Only 6% were reported from cliffs, which suggests a bias due to observer distribution. Other habitats included orchards, pasture and other farmland, parks, golf courses, and campgrounds. The Violet-green Swallow has been recorded breeding in the province from 1 April (calculated) to 24 August.

Nests:  Although the Violet-green Swallow nests solitarily, it also nests in substantial colonies, particularly on cliffs. Colony size ranged from 3 to 40 pairs (n = 16), with 8 between 5 and 15 pairs. Thirteen of the colonies were found in the interior. The Violet-green Swallow has adapted well to nesting in human-made habitats such as nest boxes, the crannies of houses, garages, sheds, barns, and other buildings, and in posts and poles, stone and brick walls, and bridges. Natural nest sites include rock cliffs, snags, and cavities in living deciduous and coniferous trees. Along the Fraser River canyon, near Williams Lake, it nests all along the cliffs, but has never used any of the more than 1,000 boxes on the adjacent plateau (A. Roberts pers. comm.). Violet-green Swallows seem to prefer boxes on buildings rather than those on poles and posts. In suburban environments, the House Sparrow frequently displaces the Violet-green Swallow from nest sites (Erskine 1979). In the Cariboo and Chilcotin areas, about half of all nests were found in natural situations. Further north, in the SubBoreal Interior and Boreal Plains, natural sites such as crevices in cliff faces and cavities in a variety of tree species were the preferred nesting sites. The adaptability of the Violet-green Swallow is indicated by the diversity of nest sites reported; any darkened cavity with an adequate entrance hole or crevice seems suitable. The species has been reported nesting inside the walls of buildings and on fiberglass bats in attics where they have gained access through knotholes or ventilation louvres, under tiles on the ridges of house roofs, between logs in log buildings, under roof shingles and flashing, in chimneys, in a trailer hitch of a semi-trailer truck, under a plywood sheet in a lumberyard, in plumbing vent pipes of buildings, and in the blasting holes of roadside rock-cuts. Sometimes a human-made site can prove to be a death trap for the birds. In the mid-1970s, dismantling of a wooden shed on the Alaksen National Wildlife Area, south of Vancouver, revealed nearly 100 swallow skeletons between the studs of a wall (R. McKelvey pers. comm.). The knothole through which they had entered was about 1.2 m up the wall, and the remains filled the space between the studs to a depth of about 0.8 m. After having gained access, the swallows, for some reason, could not return to the hole to exit. Reported nests were loosely constructed, the amount of material governed by the size of the cavity occupied. The nest was usually a collection of grasses with a small cup formed in the centre or in 1 corner of the cavity; the cup was formed with finer grasses and lined generously with feathers. White feathers seemed to be preferred. Most nests (94%; n = 515) were made of grasses and were feather-lined (80%). One nest was made entirely of feathers. Other materials included plant fibres, rootlets or twigs (6%), mud (5%), hair (3%), conifer needles, wood chips, plant down, and human-made materials such as fiberglass insulation, string, rope, and paper. Nest sites are reused in successive years. The heights of 460 nests in nest boxes ranged from 0.3 to 21 m, with 54% between 2.4 and 4.2 m; 344 nests where nest boxes were not used ranged from ground level to 78 m, with 62% between 2.4 and 6.0 m. Many of the known cliff sites have not been included in the samples. Eggs: Dates for 302 clutches ranged from 7 April to 21 July, with 51% between 29 May and 16 June. Calculated dates indicate that eggs can occur as early as 1 April and as late as 1 August. Clutch size ranged from 1 to 8 eggs (1E-13, 2E-18, 3E-20, 4E-92, 5E-117, 6E-37, 7E-4, 8E-1), with 69% having 4 or 5 eggs. The 8-egg clutch may have been the product of 2 females. The incubation period in British Columbia ranged from 14 to 17 days (n = 16), with a median of 15 days, similar to the 14 or 15 days reported by Turner and Rose (1989) and Brown et al. (1992). Nest Success: Of 188 nests found with eggs and followed to a known fate, 139 produced at least 1 fledgling, for a success rate of 74%. Coastal nest success was 76% (n = 82); interior success was 74% (n = 106). Weather and parasitism by the larvae of Protocalliphora sp. can have significant negative impact on the breeding success of the Violet-green Swallow (see also Tree Swallow and Barn Swallow). Other causes of egg or young mortality in British Columbia included predation by House Sparrows, chipmunks, squirrels, crows, deer mice, Cooper's Hawks, and American Kestrels; and nest usurpation by European Starlings, Crested Mynas, and House Sparrows. There are 2 reports of birds laying second clutches after the first brood was successfully raised; there are a number of reports of renesting following the loss of eggs. Young: Dates for 416 broods ranged from 15 April to 24 August, with 53% between 20 June and 9 July. Sizes of 353 broods ranged from 1 to 7 young (1Y-20, 2Y-50, 3Y-7, 4Y-142, 5Y-105, 6Y-26, 7Y-3), with 59% having 4 or 5 young and 76% with 3 to 5 young. The nestling period in British Columbia ranged from 23 to 27 days (n = 14), with a median of 25 days. Edson (1943) found a nestling period of 23 days. Brown-headed Cowbird Parasitism: In British Columbia, cowbird parasitism was not found in 800 nests recorded with eggs or young; the Violet-green Swallow has not been found as a cowbird host elsewhere in North America either (Friedmann et al. 1977; Friedmann and Kiff 1985).

Remarks Godfrey (1986) shows the breeding distribution of the Violet-green Swallow to include the Queen Charlotte Islands and the Taiga Plains Ecoprovince in extreme northeastern British Columbia; however, we could find no evidence that this swallow breeds in those areas. British Columbia is the centre of Violet-green Swallow breeding abundance in Canada. Yet, as Brown et al. (1992) note, "Despite an extensive distribution, less is known about the Violet-green Swallow than nearly any other North American Swallow." Their review could find no recent studies of the species' breeding biology or behaviour and was based primarily on reports from the 1940s and 1950s. Interested researchers in British Columbia have the opportunity to add to our knowledge of this species. Erskine (1979) notes that the Violet-green Swallow's ability to nest in remote cliffs and tree cavities and, at the same time, adapt well to human habitation may have saved it from harmful human impact. It readily takes to nest boxes, and once established will return year after year; an adult female banded at a nest box on 30 June 1983 at the Qualicum National Wildlife Area, Vancouver Island, was recaptured in successive years in the same or a nearby nest box until 18 June 1989. Since the Violet-green Swallow is a secondary cavity-nester, its nesting density may be limited by a scarcity of suitable nest sites in regions lacking rock cliffs (Brawn and Balda 1988). See Brown et al. (1992) for a summary of the life history of the Violet-green Swallow in North America.